Friction disk drive with pressure distributing idlers



Jan. 9, 1951 F. J. TIPPEN 2,537,559

FRICTION msx DRIVE WITH PRESSURE DISTRIBUTING IDLERS Filed April so, 1945 s Sheets-Sheet 1 ATTORIQEYS Jan. 9, 1951 F J TIPPEN 2,537,559

FRICTION DIK DRIVE WITH PRESSURE DISTRIBUTING IDLERS Filed April 50, 1945 3 Sheets-Sheet 2 I INVENTOR:

ATTORNEY-J Jan. 9, 1951 F. J. TIPPEN FRICTION DISK DRIVE WITH PRESSURE DISTRIBUTING IDLERS 3 Sheets-Sheet 3 Filed April 30, 1945 Hem.

INVENTOR:

ATTORN EYJ' Patented Jan. 9, 1951 UNITED STATES PATENT FRICTION DISK DRIVE WITH PRESSURE DISTRIBUTING IDLERS Frank John Tippen, Coventry, England Application April 30, 1945, Serial No. 591,083 In Great Britain May 5, 1944 11 Claims. 1

This invention relates to a variable speed gear of the kind which includes driving and driven discs mounted on parallel out of line shafts and frictionally coupled together by a transverse transmitting friction disc mounted for movement parallel to the faces of the driving and driven friction discs.

In gear of this kind if the contacting surface of the transverse transmission disc is a cylinder, relative rubbing motion will take place between parts of this cylindrical surface and the faces of the dri ing and driven discs, such relative motion causing wear by friction. One of the objects of the present invention is to construct a gear so that an efficient drive is maintained with a contact of minimum area between the surface of the transverse transmitting friction disc and the driving and driven disc so that such rubbing action is avoided or reduced to a minimum. Owing to the deflection of the materials under pressure contact occurs over small areas of the engaging discs but hereinafter these areas will be referred to as points of contact.

' With such an arrangement the working surfaceof the tran mitting friction disc is theoretically a line extending around the periphery, and a further object of the pre ent invention is to provide a construction wherein the p ints of contact are di per ed acro s an a preciable width of the periphery of the tran mitting friction disc T instead of lying always on the same circumferential line.

A further object of the invention is to construct the transm tting f iction di c so that any Wear that takes pl ce on it peripherv in tead of forming a fiat thereon will maintain the part Spherical characteri tic of the urface.

A further object o the invention is to construct and mount t e working faces of the driving and driven discs in such a manner that the points of cont ct with the peri hery of the tran mitting friction di c instead of lying always on the same circular line. will be di per ed over an appreciable area of the working face.

In gear of the kind referred to if slip occurs between the transmitting friction. disc and either the driving or driven discs. damage is done to the working surfaces of the parts and it is a further obiect of the pre ent invention to provide a construction wherein the possibility of such slip is greatly reduced or entirely eliminated.

A further object of the present invention is to construct the gear so that the pressures obtained between the driving and driven discs and transmission disc throuh a considerable range of speed approximate closely to the pressures theoretically required with a given co-efficient of friction for the materials used.

A further object of the present invention i to provide means to prevent the gear from being overloaded.

A further object of the present invention is to provide means whereby the necessary working pressure is obtained between the points of con-' tact of the driving disc and the transmitting disc and between the transmitting disc and the driven disc.

A further object of the present invention is to provide means for lubricating the contacting surfaces of the driving disc and transmission disc and of the contacting faces of the transmission disc and the driven disc.

Other objects of my invention will become apparent from the following description.

Referring to the drawings Figure 1 is a sectional plan view showing one construction of gear in accordance with the present invention.

Figure 2 is a sectional view upon an enlarged scale showing the construction of the driving friction disc.

Figure 3 is a sectional plan view upon an enlarged scale showing one method of applying the drive to the driving shaft.

Figure a is a plan view showing a part of the driving mechanism.

Figure 5 is a plan view showing an alternative form of driving mechanism.

Figure 6 is a sectional plan view showing another form of driving mechanism.

Figure '7 is a sectional plan view showing the driven disc and its shaft and associated parts.

Figure 8 is a sectional plan view showing a construction of balancing disc.

Figure 9 is a sectional view showing the prefer ed construction of friction transmitting disc.

Figure 10 is a perspective view of the lubricating means.

Figure 11 is a sectional view in side elevation showing an alternative construction of driving or driven disc H3 or II.

Figure 12 is a side view thereof.

In the construction shown in Figures 1 to 4 the driving disc is shown at ill and the driven disc at H. The disc It is mounted upon a shaft l2 and the disc H is mounted on a shaft !3, the sh fts l2 and I3 being parallel to each other but being out of line.

The discs If! and H are coupled together frictionallv by a friction transmitting disc 14 mounted on a shaft l5 which is parallel to the faces of the discs if! and II.

The shaft I5 is made of a material and to a a diameter which ensures that it is slightly flexible so that axial pressure from the di c In can be transmitted by t e friction transmitting disc M to the driven disc ll.

Two balancing discs .16 and I! are provided, the disc 16 engaging the driven disc H on the ass-7,659

opposite side of the centre thereof from that where the transmitting disc I4 engages, and the disc I! engages the face of the disc If! on the opposite side of the centre thereof from that where the friction transmitting disc I4 engages.

The three discs I4, I6 and If each have pe ripheral surfaces which engage the discs I9 and H and these peripheral surfaces I8 are of part spherical form so that theoretically in the sense hereinbefore referred to, the contact between each of these three discs and the faces of the discs I and I I is a point contact.

The two discs I6 and Il may be constructed as shown in Figure l or as shown in Figure 8.

The shaft I is made in two parts secured together by a coupling I9 and one part is screw threaded as shown at 20. This screw threaded part of the shaft engages in a sleeve 2| which is screw threaded internally. The sleeve 2| is mounted in a cap 22 attached to the casing 23 and the cap 22 has a cylindrical portion 24, the interior surface of which forms a guide for a rotary member 25 fixed to the shaft, the rotary member 25 having a handle 26 whereby the shaft can be rotated to produce axial movement of the disc I4.

At the opposite end the shaft I5 can slide through a sleeve which is similar to the sleeve 2! but is not threaded. This sleeve is not shown in the drawing but is mounted within a cap 2? secured to the casing 23.

Mounted on the sleeve 2i is a ball bearing 28 and the disc I! is mounted on this ball hearing. The ball bearing is retained in position on the sleeve 2| by any suitable means.

The disc I6 is mounted similarly on a bearing fixed on the projecting end of the sleeve which is mounted within the cap 21, and the whole arrangement is such that when the handle 26 is turned, the shaft I5 is moved axially but the discs I6 and I! are not moved axially but can of course rotate freely.

The discs I6 and I! may both be constructed as shown at I! in Figure l, the construction being such that the driving surface I8 is integral with the body.

Alternatively these two discs may be constructed as shown in Figure 8 wherein the body if is provided with a ball bearing 28 and carries a replaceable tyre 29 retained in position by nuts 30 screwing on to a threaded part 3| of the body 1?.

The transmitting disc I4 may also be constructed with its driving surface I8 intgeral with the body. It is however preferred to use the construction shown in Figure 9 wherein the body 32 is provided with a peripheral flange 33 opposite sides 34 and 35 of which are obliquely disposed in relation to a plane which is at right angles to the axis of the body 32.

Rings 36 and 31 are detachably secured against the shoulders 34 and 35, the opposed surfaces of these rings being in line with the shoulders 34 and 35 and between the rings is mounted a renewable tyre 38, this tyre bearing on a cylindrical surface 39 on the body, the axis of which is inclined to the axis of the body.

The body is mounted on a ball bearing 48 mounted on a flanged collar 4| fixed to the shaft l5 so that endwise movement of the shaft I5 is transmitted to the disc 54. The tyre 38 can creep circumferentially on the body as the disc rotates with the result that the points of contact between the tyre and the two discs I0 and II become spread over an appreciable width of the part spherical engaging surface 42, thus distributing the wear over a considerable area instead of it being confined to a circumferential line. Further with this arrangement the periphery of the tyre 38 will not tend to wear flat. The part spherical shape of the surface 42 will continue to be retained even if wear takes place.

The surfaces of the discs I8 and II may be lubricated by the lubricator shown in Figure 10, this lubricator comprising a bracket 43 having upwardly projecting arms 44 to which are secured absorbent wick members 45, the ends 43 of which are in light pressure contact with the surfaces of the discs It and I I.

This lubricating element is placed in the base of the casing 23 and may if desired be fixed thereto and a suitable quantity of parafiin or other lubricant is placed in the casing 23.

The discs Ill and H may both be provided with renewable wearing faces formed by plates 41 shown in Figure 2, the plates 4'7 being attached each by a sore. 48 engaging a plate 54 at the back of the disc and the plates 41 being prevented, if desired, from rotating relatively to the discs It and i i by a dowel 49.

Instead of using the construction shown in Figure 2 either the disc It] or Ii, or both, may be constructed as shown in Figures 11 and 12 wherein the face of the disc I0 is provided with a circular recess :49 which is eccentric in rela tion to the periphery of the disc and mounted in this eccentric recess is a face plate I4I. This face plate is mounted on a boss I42 which is concentric with the recess I40 but eccentric in relation to the periphery of the disc.

The face plate MI is retained against the bottom of the recess by a screw and washer as shown.

With this arrangement the face plate MI is able to creep around the center of the boss I42 during the working of the gear with the result that the points of contact between the friction transmitting disc I4 and the plates I4I will not all lie upon a circular line but will become dispersed over an appreciable area of the plate I4l.

Further the disc I6 is of hollow construction at the back and is provided with a somewhat resilient plate 58 by which the disc is secured by a flange 51 on the driving shaft I2. The end of the driving shaft which may be of part spherical form may engage a flange 43 on the plate 54 engaging the body of the disc I0.

It will be appreciated that a certain pressure is necessary in an axial direction on the disc II in order that it may drive the disc I4, and this pressure is mainly transmitted to the disc l0 by the driving shaft I2 through the plate 54. The plate 53 provides for a slight resilience in the structure of the driving disc which is loaded axially at the centre in one direction and in the opposite direction at two offset position where it engages the discs I4 and IT. The pressure required to transmit a given torque varies inversely in accordance with the distance between the centre of the disc I 0 and its point of contact with the disc I4 and these conditions are substantially met by the manner of loading and supportin the disc I0.

The driving shaft i2 extends through a sleeve 55 which is adapted to be driven together with the shaft. For a portion of its length 56 the shaft 52 is of reduced diameter whereby it is ermitted to make slight bending movements during its operation.

Thus the desired resilience of the structure of the driving element may be provided by the plate 50 or by the reduced section of the part 56 or both may contribute to it. This resilience permits the pressure of the driving disc II! on the transmitting disc I4 to be an inverse function of distance between the point of contact between them and the centre of the driving disc bearing in mind that the balancing disc I? is at a constant distance from the centre of the driving disc. This makes an important contribution towards maintaining the torque transmitting capacity of the gear a the transmitting disc approaches the centre of the driving disc.

The provision of the resilient plate 50 and the reduced portion 55 of the driving shaft I2 are shown as applied to the driving disc I9. Similar provision may be made to the driven disc II and the shaft I3.

The shaft I2 extends through an opening in one end of the casing, which opening is closed by a cap 5'! having a tubular extension 58 carrying a pair of spaced ball bearing 59, 69 in which the sleeve 55 is mounted.

The ball bearing 69 is retained in position by a plate 63 secured to the end of the tubular part 58 of the cap 51.

The end of the sleeve 55 has an enlarged portion 59 and a flange 65 and this flange 65 is secured by screws 55 to a hollow shaft 61 upon which is mounted a driving pulley '58. The inner part of this driving pulley is mounted between a ring 69 and a second ring it acted upon by compression springs II which abut against an adjustable ring I2 so that the pressure of the springs i I can be adjusted.

The ring I2 is locked in position by an end cap 13 screwing on to the hollow shaft 61.

The arrangement is such that the torque imparted to the pulley 69 is frictionally transmitted to the unit formed by the hollow shaft 9'! and the sleeve 55. The pressure of the springs II can be adjusted so that the torque which can be applied to the rotating unit which includes the shaft I2, can be kept down to a predetermined limit.

The end of the shaft I2 is provided with a driving dog M which engages in a slot in the end of a sleeve ?5 having a flange I6. The end face of this flange is formed as a cam having two spaced concavities.

Mounted between the flange 55 on the end of the sleeve 55 and a flange TI on the end of the hollow shaft 62' is a second cam member 19 having its end face formed with two spaced concavities. Two balls I9 are placed between the two pairs of concavities in the members I6 and I8 with the result that when the member 18 is rotated with the unit 61, 55, rotary motion is imparted to the shaft 12 accompanied by an axial thrust produced by the cam surfaces acting through the balls I9, which axial thrust is proportional or approximately proportional to the torque. In this way the disc II) has applied to it an axial thrust against the disc I 9.

An initial axial load on the shaft I2 is produced by a spring 89 acting between a flange SI on an adjustable pin 82, and a flange 83 on a pin 84 bearing on the end of the sleeve I5 which is secured to the end of the shaft I2 by means of the screw 85.

The pin 82 has a screw threaded portion 89 engaging in a tapped hole in the cap I3 in order that the pressure of the spring 89 may be adjusted.

An alternative method of imparting the drive to the shaft I2 accompanied-by anend thrust tional endwise load on the shaft I2.

6 which i proportional or approximately proportional to the torque is to replace the members I5 and I8 shown in Figure 4 by the members 81 and 88 shown in Figure '5. The member 81 is provided with two V-shaped projections 89 which engage in 'v-shaped recesses 99 in the member 88', these projections and recesses forming cam surfaces which produce the endwise thrust.

A further alternative is shown in Figure 6 wherein the sleeve I5 is replaced by a pin 9| having a screw threaded portion 92 engaging in a sleeve 93 having a thread on its interior and another thread 94 of opposite hand on it exterior. This thread 94 engages an interior thread in an outer sleeve 95 secured between the flange 65 of the sleeve 55 and the flange TI on the hollow driving shaft 61. g

This device consisting of the outer sleeve 95, an intermediate sleeve 93 and the threaded part 92 of the pin 9I is designed to impart to the shaft I2 an endwise thrust which is proportional or approximately proportional to the torque for either direction of rotation of the pulley '68.

It should be noted that the devices shown in Figures 4 and 5 also impart an endwise thrust on the shaft I2 in the same direction for either direction of rotation of the pulley 69.

The end of the intermediate threaded member 93 is engaged by a washer I 9! upon which acts a compression spring I02, the opposite end of which engages a washer I03 placed between the end of the driving shaft '91 and the cap I3. The washer I I]! is thus spring loaded in the direction towards the disc It.

In operation when the pulley 68 is driven in one direction relative rotary motion takes place between the members 95 and 93 so that the latter moves in an endwise direction until the washer I9I engages the shoulder M24; in the hollow shaft 5'! and thereafter the members 95 and 93 rotate together and impart an endwise thrust in the required direction to the pin 9!. The spring I92 is then dormant.

The pin 9! is attached to the end of the shaft I2 by means of a screw 95 and the head 91 of the screw is engaged by a cap 99 on which acts a second compression spring 99 providing an addi- The spring 99 abuts against a screwed pin I95 screwing into the cap I3 so that the pressure of the spring can be adjusted. This spring pressure continues to act under all conditions.

When the pulley 98 is driven in the opposite direction it tends to move the intermediate sleeve 93 to the left as shown in Figure 6 so that an endwise force is applied thereby to the pin 9|. With any of these arrangements an endwise thrust to the left as shown in Figures 1 and 3 is produced on the shaft I2 and a corresponding reaction is set up as an axial thrust to the right in the sleeve 55. This axial thrust is transmitted to the inner race of the bearing 59.

Acting between the outer races of the two ball bearings. 59, 99 is a compression spring 6| so that the axial thrust applied to the bearing 59 by the sleeve 55 is transmitted to the other bearing. Further, a distance tube 52 is placed between the inner races of the two ball bearings, this distance tube 'eing mounted on the sleeve 55.

Referring to Figure l the driven shaft I3 is supported in ball bearings 13a and I99 carried in the sleeve I95 having a flange I95 upon which acts a compression spring I91 engaging a shoul. der I08 in a cap I99 secured in an opening in the casing 23. A distance tube III) is placed on the shaft I3 between the bearings "33a and I04.

' cates the bearings.

The shaft I3 is provided with a tapered portion [I202 on which is mounted a driven pinion H3, the pinion being spring loaded by a spring II4 on to the tapered part of the shaft. The pressure of the spring ii can be adjusted by turning a nut II5 screwing on to a reduced part on the end of the shaft 2a. In this way the value of the torque which can be transmitted can be limited to a predetermined figure.

Mounted on the tubular part III of the cap IE9 is a bracket H6 to which is attached a casing member l if having a tubular part I I8 carrying bearings H3 in which is mounted a driven shaft I29 carrying a pulley I2I by which power .may be taken off.

The shaft I29 carries a gear wheel E22 gearing with the pinion I 53.

An alternative arrangement is shown in Figure '7 wherein the driven shaft i3 is provided with a reduced extension I23 which is screw threaded, the thread being engage by a threaded sleeve :24. The sleeve I24 has an exterior thread which engages a thread in the sleeve E25. This sleeve I25 is provided with a flange I26 which is secured by screws I2? between a flange I 23 on a sleeve I29 mounted on the shaft 93 and a flange I36 formed on a tapered shaft I3 I.

The screw threads on the shaft part I23 and in the sleeve 525 are of opposite hand and the device has the sam object as that described with reference to Figure 6, i. e. for either direction of rotation of the driven disc II an endwise reaction is produced on the shaft I3 towards the disc II.

The sleeve !29 is supported in the bearings I32 and I33 mounted in the sleeve I05 and the sleeve I05 is spring loaded by the spring I6! while a further spring $38 operates between the two outer races of the ball bearings. The purpose of the spring 38 is to ensure that the axial thrust on the sleeve is shared by the outer races of the two bearings I32 and I33.

In operation when the disc II is driven in one direction an endwise thrust to the right as shown in Figure 7 is produced by the engagement of the threaded part I23 of the shaft is with the intermediate sleeve I24. When the disc II is driven in the opposite direction an endwise thrust on the shaft 53 to the right as shown in Figure '7 is produced by the action of the external thread on the intermediate sleeve I24 with the thread in the member 125 which is fixed to the sleeve !29.

The arrangements described and shown for producing an endwise thrust in the shaft I2 proportional to the torque applied to the shaft may be duplicated for the driven shaft E3, the endwise thrust in the latter case being towards the transmission disc I4.

What I claim then is:

1. Variable speed gear of the kind specified comprising a driving disc of resilient construction, a friction transmission disc engagingthe face of said driving disc, means for loading said driving disc in an axial direction, and a balancing disc engaging the driving surface of the driving disc on the opposite side of its centre of rotation from that at which the friction transmission disc engages, and at a fixed distance from the axis of the driving disc, whereby the axial load on said driving disc is distributed between the friction transmission disc and said balancing disc.

2. Variable speed gear of the kind specified comprising a driving disc mounted resiliently, means for loading said driving disc in an axial direction, a friction transmission disc engaging the face of said driving disc and balancing disc engaging the driving surface of the driving disc on the opposite side of its centre of rotation from that at which the friction transmission disc engages, and at a fixed distance from the axis of the driving disc, whereby the axial load on said driving disc is distributed between the friction transmission disc and said balancing disc.

3. Variable speed gear of the kind specified comprising a driving disc, a driven disc of resilient construction, means for loading the driving disc in an axial direction a friction transmission disc engaging the faces of said driving and driven discs, and a balancing disc engaging the driven disc on the opposite side of its centre of rotation from that at which the friction transmission disc engages, and at a fixed distance from the axis of the driving disc, whereby the axial load on said driven disc is distributed between the friction transmission disc and said balancing disc.

4. Variable speed gear of the kind specified comprising a driving disc, a driven disc mounted resiliently, means for loading the driving disc in an axial direction a friction transmission disc engaging the faces of said driving and driven discs, and balancing disc engaging the driven disc on the opposite side of its centre of rotation from that at which the friction transmission disc engages, and at a fixed distance from the axis of the driving disc, whereby the axial load on said driven disc is distributed between the friction transmission disc and said balancing disc.

5. Variable speed gear of the kind specified comprising a driving disc of resilient construction, a friction transmission disc engaging the face of said driving disc, said disc having a hollow back across which is secured a resilient plate, to the centre of which is a flange to which a shaft is secured, means for loading said driving disc in an axial direction, said load being transmitted to the disc partially by said resilient plate at its periphery and partly by said flange at the centre, and a balancing disc engaging the driving surface of the driving disc on the opposite side of its centre of rotation from that at which the friction transmission disc engages, and at a fixed distance from the axis of the driving disc, whereby the axial load on said driving disc is distributed between the friction transmission disc and said balancing disc.

' 6. Variable speed gear of the kind specified comprising a driven disc of resilient construction, said disc having a hollow back across which is secured a resilient plate, to the centre of which is a flange to which a shaft is secured, means for loading said driven disc in an axial direction, said load being transmitted to the disc partially by said resilientplate at its periphery and partly by said flange at 'the centre a friction transmis- .sion disc engaging the face of said driving disc and a balancing disc engaging the driven'disc on the opposite side of its centre of rotation from that at which the friction transmission disc engages, and at a, fixed distance from the axis of the driving disc, whereby the axial load on said driven disc is distributed between the friction transmission disc and said balancing disc.

7. Variable speed gear of the kind specified comprising a casing, bearings supported in opposite sides of said casing, said bearings being par allel but out of alignment, a driving shaft in one bearing, driven shaft in the other bearing, a driving disc on the driving shaft and within the casing, a driven disc on the driven shaft and within the casing, a transverse shaft within the casing extending between and parallel to the faces of the driving and driven discs, a friction transmission disc mounted for rotation on said transverse shaft and engaged on opposite sides by the driving and driven disc, means for preventing endwise movement of the friction transmission disc on the transverse shaft, means for adjusting the transverse shaft in an endwise direction, sleeves in opposite sides of the casing and concentric with the transverse shaft, and balancing discs mounted for rotation on said sleeves, one of these discs engaging the driving disc and the other engaging the driven disc, said balancing discs engaging respectively the driving and driven discs at positions on the opposite sides of the centres of their rotation from that at which the friction transmission disc engages them.

8. Variable speed gear of the kind specified comprising a casing, bearings supported in opposite sides of said casing, said bearings being par allel but out of alignment, a driving shaft in one bearing, a driven shaft in the other bearing, a driving disc on the driving shaft and within the casing, a driven disc on the driven shaft and within the casing, a transverse shaft within the casing extending between and parallel to the faces of the driving and driven discs, a friction transmission disc mounted for rotation on said transverse shaft and engaged on opposite sides by the driving and driven discs, means to prevent relative movement between the friction 4 transmission disc and the transverse shaft parallel to the axis of the said shaft, means for adjusting the transverse shaft in an endwise direction, balancing discs mounted for rotation each on an axis disposed at right angles to the faces of the driving and driven discs and supporting means on the casing for the balancing discs, said balancing discs engaging respectively the driving and driven discs at positions on the opposite sides of the centres of their rotation from that at which the friction transmission disc engages them.

9. Variable speed gear of the kind specified comprising a casing, bearings supported in opposite sides of said casing, said bearings being parallel but out of alignment, a driving shaft in one bearing, a driven shaft in the other bearing, a driving disc on the driving shaft and within the casing, a driven disc on the driven shaft and within the casing, a transverse shaft within the casing extending between and parallel to the faces of the driving and driven discs, a friction transmission disc mounted for rotation on said transverse shaft and engaged on opposite sides by the driving and driven discs, means to prevent relative movement between the friction transmission disc and the transverse shaft parallel to the axis of the said shaft, means for adjusting the transverse shaft in an endwise direction, balancing discs mounted for rotation each on an axis disposed at right angles to the faces of the driving and driven discs, supporting means on the casing for the balancing discs, and means for preventing said balancing discs from moving parallel to the faces of the driving and driven discs, said balancing discs engaging respectively the driving and driven discs at positions on the opposite sides of the centres of their rotation from that at which the friction transmission disc engages them.

10. Variable speed gear of the kind specified comprising driving and driven discs mounted on parallel out of line shafts, said discs being frictionally coupled together by a transmission friction disc mounted on a shaft which is parallel to the faces of the driving and driven discs and disposed between them, said transmission disc being movable parallel to said faces, a driving disc of resilient construction, means for loading said driving disc in an axial direction, balancing discs mounted coaxially with the shaft which carries the transmission friction disc, one of said balancing discs engaging the driving disc, and the other of said balancing discs engaging the driven disc and means for preventing said balancing discs from moving parallel to the faces of the driving and driven discs.

11. Power-transmission mechanism comprising a pair of discs mounted upon shafts which are arranged transversely to each other, one disc having a circular recess in its working face, which recess is eccentric in relation to the axis of the shaft upon which the disc is mounted, a boss on the disc at the centre of the recess, a circular plate mounted for rotation on said boss in said recess, and means for retaining said plate in the recess, and the other disc comprising a hollow body, a bearing in the body for engaging means rotating with the shaft supporting the disc, said body having an exterior bearing surface, the axis of which intersects the axis of the bearing in the body and is inclined thereto at a small angle, a tire mounted on said exterior bearing surface and capable of rotating relatively to the body, said tire having a, periphery of part-spherical form, the radius of which is equal to the radius of said periphery, and means for preventing said tire from moving axially on the body, the periphery of said tire engaging the circular plate of 60 the other disc.

FRANK JOHN TIPPEN.

REFERENCES CITED The following references are of record in the 55 file of this patent:

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